Radiation units are divided into two categories: activity units and radiation dose units, both of which are promulgated by the International Commission for Radiation Units and Measurements (ICRU) and are called International System Units (SI units). The following briefly describes several important radiation units:

Activity

The number of spontaneous decays of a radionuclide in a unit time, that is, the decay rate, is called the radioactivity. The unit of activity is "beque", abbreviated as Bq, which is defined as: 1 beque (Bq) = 1 decay/sec

Beque is used to express the intensity (decay rate) of a radiation source (such as cobalt 60).

Another commonly used old unit is "Curie": 1 Curie (Ci) = 3.7×10 Bq (Bq)10.

Absorbed dose, D

The radiation energy (joules) absorbed by a unit mass of matter (kg) is called the absorbed dose. The unit of absorbed dose is "Grey", abbreviated as Gy, which is defined as

1 Gray (Gy) = 1 Joule/kg

The average absorbed dose per hour is called the absorbed dose rate, in units of Gray/hour (Gy/h), milligy/hour (mGy/h), micro-Gy/hour (μGy/h). To

Equivalent dose (dose equivalent), HT

Different types of radiation (α, β, γ, neutrons) irradiate the human body, although the human body has the same absorbed dose, but it will cause different harmful phenomena. For this reason, radiation weighting factors (Q) are determined for different types of radiation, which represent different degrees of biological damage to human tissues caused by different radiation.

The equivalent dose is the product of the absorbed dose of the human body and the radiation weighting factor, which already contains the meaning of radiation harm to the human body. Its unit is "Sievert", abbreviated as "Xi", abbreviated as Sv, which is defined as:

H(Sievert)=D(Grey)×Q T

There are also millisieverts (mSv) and microsieverts (μSv). We took a chest X-ray, and the chest tissue received a dose of approximately 0.1 mSv. It can be seen from the radiation weighting factor Q value that although alpha particles have weak penetrating power, they have great health hazards. If the isotope of radioactive alpha particles such as uranium 235 is eaten into the body, it will cause greater damage to the tissues in the body.

Effective dose (effective dose), E

Since various tissues and organs of the human body have different sensitivity to radiation, although they receive the same equivalent dose, the risk (probability) of health loss (cancer or bad inheritance) is different, that is to say, different tissues and organs are exposed to The same radiation causes different damage. Therefore, a "tissue weighting factor" (WT) was established to represent the probability of health loss of each tissue and organ receiving radiation. To

If the equivalent dose (HT) of each tissue and organ is added up by the product of its weighting factor, it becomes the effective dose (E). E represents the whole body radiation dose, used to assess the risk of radiation that may cause our health effects, and the unit is also sievert (Sv).